Projection objective for microlithography

ABSTRACT

A projection objective for microlithography is used for imaging an object field in an object plane into an image field in an image plane. The projection objective comprises at least six mirrors of which at least one mirror has a freeform reflecting surface. The ratio between an overall length (T) of the projection objective and an object image shift (d OIS ) can be smaller than 12. The image plane is the first field plane of the projection objective downstream of the object plane. The projection objective can have a plurality of mirrors, wherein the ratio between an overall length (T) and an object image shift (d OIS ) is smaller than 2.

CROSS-REFERENCE TO RELATED APPLICATIONS

Under 35 U.S.C. §120, this application is a continuation of and claimspriority to International Application No. PCT/EP 2009/001 448, entitled“PROJECTION OBJECTIVE FOR MICROLITHOGRAPHY,” filed on Feb. 28, 2009,which claims priority to German Patent Application No. 10 2008 000800.1, filed on Mar. 20, 2008 and the German Patent Application No. 102008 033 342.5, filed on Jul. 16, 2008. The entire contents of each ofthe above-referenced applications is incorporated herein by reference.

FIELD OF THE DISCLOSURE

The disclosure relates to a projection objective for microlithography.Furthermore, the disclosure relates to an optical system, in particularincluding a projection objective of this type, a projection exposureapparatus including an optical system of this type, a method ofproducing a microstructured component using a projection exposureapparatus of this type, and a microstructured component which isproduced according to this method.

BACKGROUND

Examples of projection objectives for microlithography are disclosed inU.S. Pat. No. 6,266,389 B1, in US 2005/0134980 A1, in US 2007/0195317A1, in US 2007/0058269 A1, in US 2007/0223112 A, in U.S. Pat. No.6,396,067 B1, in U.S. Pat. No. 6,361,176 B1 and in U.S. Pat. No.6,666,560 B2.

SUMMARY

Conventional projection objectives are still in need of improvement interms of their total transmission, in terms of an unwanted apodizationand in terms of their space requirements, in particular if they are usedwith EUV illumination light.

In certain aspects, the invention features projection objectivesexhibiting improved total transmission and reduced or avoided negativeapodization effects. As an alternative or in addition thereto, theprojection objectives can be relatively compact.

According to one aspect of the invention, the projection objective isprovided with at least six mirrors, wherein at least one of the mirrorshas a freeform surface, and wherein the ratio between the overall lengthof the projection objective and the object image shift of the projectionobjective is smaller than 12. A projection objective of this type mayhave an intermediate image plane between the object plane and the imageplane. This allows given imaging requirements to be fulfilled whileminimizing the dimensions of the individual mirrors, in other words oftheir absolute reflecting surface. In embodiments with an intermediateimage plane, it is possible to use mirrors with relatively small radiiof curvature. Furthermore, objective designs are conceivable in which arelatively large working distance can be maintained between the exposedreflecting surfaces and the imaging beams passing by the mirrors. Theobject image shift may have an absolute value which is greater than 120mm (e.g., greater than 150 mm, greater than 200 mm).

According to another aspect of the invention, the projection objectivehas at least six mirrors of which at least one mirror has a freeformreflecting surface. The image plane of this projection objective is thefirst field plane of the projection objective downstream of the objectplane. If, accordingly, an intermediate image plane between the objectplane and the image plane of the projection objective is dispensed with,this can allow a spectrum of incidence angles, in other words adifference between a largest and a smallest incidence angle of imagingbeams impinging upon a respective one of the mirrors, to be kept small.In general, this reduces the demands on a reflective coating on themirrors. The reflective coating may then either be optimized in terms ofa high peak reflection or in terms of an even reflection across themirror surface, wherein severe variations of incidence angles on one ofthe mirrors can be neglected in practice. In certain embodiments, theresult is a projection objective with a good total transmission whichallows the unwanted effect of an apodization to be avoided or reduced.If at least one mirror is designed as a freeform reflecting surface,projection objectives can show minor imaging errors even if nointermediate image plane is provided. The at least six mirrors of theprojection objective allow imaging errors to be corrected easily. Insome embodiments, projection objectives may be a mirror projectionobjective (i.e., a catoptric projection objective), in other words aprojection objective in which all imaging-beam guiding components arereflective components.

In certain embodiments, projection objectives are characterized by aration between their overall length (T) and an object image shift(d_(OIS)) which is smaller than 5. Such projection objectives can becompact and ensure a good separation of the object field from the imagefield. The ratio between the overall length and the object image shiftcan be smaller than 2 (e.g., smaller than 1.5, smaller than 1.1).

In some embodiments, projection objectives include a mirror having afreeform reflecting surface. A freeform reflecting surface can allowimaging errors to be minimized by the projection objective. Other typesof freeform surface are conceivable as well. Freeform surfaces cannot bedescribed using a function which is rotationally symmetric with respectto a marked axis which is a normal to a surface area of the mirrorsurface. In particular, freeform surfaces cannot be described using anasphere equation of the type describing a conic section; furthermore, atleast two independent parameters are needed in order to describe themirror surface. The shape of a boundary of the optically active mirrorsurface is not important when characterizing a mirror surface as afreeform surface since it is the shape of the surface itself, not itsboundary, that determines whether the mirror has a freeform surface.Indeed, a mirror surface can be described using a rotationally symmetricfunction while the surface boundary is not rotationally symmetric inshape.

In some embodiments, projection objectives include a plurality ofmirrors and have a ratio of T to d_(OIS) that is smaller than 2. Suchprojection objectives can ensure a good separation of the object fieldfrom the image field. The ratio of T to d_(OIS) can be smaller than 1.5and, more preferably, smaller than 1.1. The projection objectives can becatoptric projection objectives.

According to another aspect of the invention, projection objectives canhave a plurality of mirrors of which at least one mirror has a freeformreflecting surface, and at least one intermediate image plane betweenthe object plane and the image plane, wherein the ratio between anoverall length (T) of the projection objective and an object image shift(d_(OIS)) is smaller than 12. By using the at least one freeformreflecting surface, a distinct object image shift may even be achievedin a projection objective having an intermediate image plane. This mayin particular serve to guide the illumination light past furthercomponents of a projection exposure apparatus which is equipped with theprojection objective without having to make compromises on the incidenceangles impinging the mirrors of the projection objective. In particular,virtually all reflections of the illumination light may be achieved withsmall incidence angles or, alternatively, very large incidence angles(grazing incidence). The intermediate image plane of the projectionobjective can allow bundles of the imaging light to be guided betweenthe object plane and the image plane, with the bundles having typicalbundle dimensions or bundle diameters which, except for the bundleswhich are guided in the vicinity of a last mirror which defines thenumerical aperture of the projection objective, are comparatively small.This may facilitate reduced vignetting during a projection exposureusing the projection objective. Furthermore, a projection objectiveincluding at least one intermediate image plane has at least two pupilplanes of which one is arranged between the object plane and the atleast one intermediate image plane while the other is arranged betweenthe at least one intermediate image plane and the image plane. This canenhance the possibilities of controlling illumination parameters byinfluencing the bundles in or adjacent to the pupil planes.

In some embodiments, projection objectives are characterized in that thedistance between a chief ray of a central object field point and anormal to the object plane, the normal passing through the centralobject field point increases monotonically along a path of the chief raywhich starts at the object field and propagates to the image field. Apath of the chief ray allocated to the central object field point canallow a large object image shift to be achieved on the mirrors of theprojection objective with small to medium incidence angles. In the caseof such a chief ray path, there is no portion of the path of the chiefray where the chief ray is guided back in the direction of the normal,which would be counterproductive for achieving a large object imageshift.

In some embodiments, projections objectives have an object image shiftgreater than 200 mm. Absolute values of the object image shift can beadvantageous for spatially separating an illumination light beam pathupstream of the object field of the projection optics from the imagingbeam path in the projection objective.

Projection objectives can be characterized by a ratio of a differencebetween a largest (α_(max)) and a smallest (α_(min)) incidence angle ofimaging beams impinging upon one of the mirrors on the one hand to anumerical aperture on the image side of the projection objective on theother amounts to a maximum of 60°.

The ratio between a spectrum of incidence angles and a numericalaperture on the image side can result in advantageously low demands onreflective coatings on the mirrors. The spectrum of incidence angle canamount to a maximum of 15° (e.g., a maximum of 13°, a maximum of 12°, amaximum of)10°. Accordingly, the ratio between the spectrum of incidenceangles and the numerical aperture on the image side of the projectionobjective preferably amounts to a maximum of 60° (e.g., a maximum of52°, a maximum of 48°, a maximum of)40°. A numerical aperture on theimage side of 0.25 may be provided. Other numerical apertures on theimage side in the range between 0.25 and for instance 0.9, i.e. anumerical aperture on the image side of for instance 0.3, 0.4, 0.5, 0.6,0.7, 0.8 or 0.9, may be provided as well; this will cause the ratiosbetween the spectrum of incidence angles and the numerical aperture onthe image side of the projection objective to change accordingly.

Projection objectives having a numerical aperture (NA=n sin α, with n:refractive index, for instance that of flushing gas, α: half apertureangle of the objective on the image side) of at least 0.25 can result ina good spatial resolution of the projection objective. The differencebetween a largest and a smallest incidence angle of imaging beamsimpinging upon one of the mirrors of the projection objective can amountto a maximum of 0.9 arcsin(NA) (e.g., a maximum of 0.8 arcsin(NA), amaximum of 0.7 arcsin(NA)).

Projection objectives can have fields dimensions of at least 2 mm×26 mm.Such field sizes can ensure a good throughput when operating aprojection exposure apparatus including a projection objective of thistype.

Projection objectives can exhibit an incidence angle (β) of an imagingbeam allocated to a central object field point on the object field inthe range between 5° and 9°. Such an incidence angle can allow areflection mask to be used on which is disposed the structure that is tobe imaged using the projection objective. In some embodiments, theincidence angle amounts in particular to 6°.

Among other advantages, embodiments can improve an optical systemincluding a projection objective and an illumination system formicrolithography for guiding illumination light emitted by a lightsource and for illuminating an object field in such a way thatreflection losses are reduced to a minimum when guiding the illuminationlight. For example, embodiments can include an optical system includingan illumination system for microlithography for guiding illuminationlight which is emitted by a light source, and for illuminating an objectfield, a projection objective for imaging the objective field into animage field, wherein the illumination system is designed in such a waythat the illumination light has an intermediate focus between the lightsource and the object field, and the optical system is characterized bya ratio between an overall length (T) of the projection objective and anintermediate-focus image shift (D) which is smaller than 5.

Such a ratio between the overall length of the projection objective andthe intermediate-focus image shift may guarantee that the illuminationlight can be guided past components which large space requirements onthe image side without requiring any additional illumination lightguiding optical components and without requiring extreme incidenceangles which might reduce throughput. The ratio between the overalllength of the projection objective and the intermediate-focus imageshift may be smaller than 3, smaller than 2, smaller than 1.90, smallerthan 1.80 and may in particular amount to 1.75. Even smaller ratios areconceivable as well.

A typical space requirement on the image side, when measured in an imageplane in the center of the image field, amounts to approximately 1 m, inparticular also in the direction of components of the illuminationoptics, and approximately 1 m as well when measured perpendicular to theimage plane away from the image plane.

In some embodiments, having an intermediate focus in the illuminationsystem arranged in a vicinity of an opening of a mirror in theillumination system can enable the illumination light to be guided withparticularly small maximum incidence angles impinging the components onthe illumination system.

In some embodiments, the illumination system includes a collector and amaximum of three mirrors. Such a design of the illumination system canhave a high illumination light throughput due to the low number ofreflecting components. The illumination system may in particular have acollector and only two additional mirrors, in other words only twoadditional reflecting components.

Advantages of the projection objectives, of the optical system and ofthe projection exposure apparatus become apparent in particular when EUVlight is used as illumination light.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will hereinafter be explained in more detail by means of thedrawing in which:

FIG. 1 shows a diagrammatic view of a projection exposure apparatus formicrolithography;

FIG. 2 shows a meridional section containing exemplary imaging beampaths through an embodiment of a projection objective;

FIG. 3 shows a similar view to FIG. 2 of another embodiment of aprojection objective;

FIG. 4 shows a similar view to FIG. 2 of another embodiment of aprojection objective;

FIG. 5 shows a similar view to FIG. 2 of another embodiment of aprojection objective;

FIG. 6 show a diagrammatic view of a projection exposure apparatusincluding the projection objective shown in FIG. 5; and

FIG. 7 shows a similar view to FIG. 6 of another embodiment of aprojection exposure apparatus including the projection optics accordingto FIG. 5.

DETAILED DESCRIPTION

A projection exposure apparatus 1 for microlithography includes a lightsource 2 for illumination light 3. The light source 2 is an EUV lightsource which generates light in a wavelength range between 5 nm and 30nm. Other EUV wavelengths are conceivable as well. Alternatively, theprojection exposure apparatus 1 may also be operated using for instanceillumination light 3 with visible wavelengths, UV wavelengths, DUVwavelengths or VUV wavelengths. A beam path of the illumination light 3is shown very diagrammatically in FIG. 1.

The illumination light 3 is guided to an object field 4 in an objectplane 5 using an illumination system 6 (also referred to as illuminationoptics 6). A projection optics 7 in the form of a projection objectiveis used to image the object field 4 into an image field 8 in an imageplane 9 at a given reduction ratio. This reduction ratio is 4:1. Whenimaged into the image field 8, the object field 4 is thus reduced insize by a factor of 4 using the projection optics 7.

The projection optics 7 reduces images by a factor of 4, for example.Other image scales are conceivable as well, for instance 5×, 6×, 8×, oreven image scales which are greater than 8×. Image scales which aresmaller than 4× are conceivable as well.

The image plane 9 is parallel to the object plane 5. In this process, aportion of the reflection mask 10 is imaged which coincides with theobject field 4. Said portion is imaged onto the surface of a substrate11 in the form of a wafer which is carried by a substrate holder 12.

In order to facilitate the description of positional relationships, thedrawing includes an xyz coordinate system. In FIG. 1, the x-axis isperpendicular to the drawing plane and runs away from the viewer intothe drawing plane. The y-axis extends to the right of FIG. 1. The z-axisextends downwardly in FIG. 1.

The reflection mask 10, which is held by a reticle holder (not shown),and the substrate 11 are scanned synchronously in the y-direction duringthe projection exposure.

FIG. 2 shows a first embodiment of an optical design of the projectionoptics 7, the Figure showing the path of individual imaging beams 13 ofthe illumination light 3 which are emitted by two spaced field points.One of these imaging beams 13 is the chief ray of the central fieldpoint, in other words the chief ray of the field point which liesexactly on the intersection of the diagonal which joins the corners ofthe object field 4 or of the image field 8.

In the projection optics 7, the image plane 9 is the first field planeof the projection optics 7 downstream of the object plane 5. In otherwords, the projection optics 7 does not have an intermediate imageplane.

The projection optics 7 has a numerical aperture of 0.25 on the imageside. An overall length T, in other words the distance between theobject plane 5 and the image plane 9 of the projection optics 7, amountsto 1,585 mm.

In some embodiments of projection optical systems (not shown) in whichthe object plane 5 is not parallel to the image plane 9, the overalllength T is defined as the distance of a central field point from theimage plane. In certain embodiments, a projection objective (not shown)which is equipped with an uneven number of mirrors, for instance sevenor nine mirrors, the overall length is defined as the maximum distancebetween one of the mirrors and one of the field planes.

An object image shift d_(OIS) of the projection optics 7 amounts to1,114.5 mm. The object image shift d_(OIS) is the distance of aperpendicular projection P of a central object field point onto theimage plane 8 from the central image point.

In the projection optics according to FIG. 2, the ratio between theoverall length T and the object image shift d_(OIS) therefore amounts toapproximately 1.42.

The field size of the projection optics 7 in the image plane 9 amountsto 2 mm in the y-direction and 26 mm in the x-direction while in theobject plane 5, the field size amounts to 8 mm in the y-direction and108 mm in the x-direction.

The object field 4 and the image field 8 are rectangular. The fields maygenerally also have the shape of a sector of a circle with acorresponding xy aspect ratio, in other words they may also have acurved shape.

The y-dimension of the fields is also referred to as slot height whilethe x-dimension is also referred to as slot width.

An incidence angle β of the imaging beams 13 impinging upon the objectfield 4, in other words on the reflection mask 10, amounts to 6°. Otherincidence angles β are conceivable as well.

The projection optics 7 includes a total of six mirrors M1, M2, M3, M4,M5, M6 which are numbered in the order in which they are exposed to theillumination light 3. The mirrors M3 and M6 are concave. The mirror M4is convex. It shall be noted that FIG. 2 only shows the reflectingsurfaces of the mirrors M1 to M6; other aspects such as the entiremirror bodies or associated holders are omitted.

The mirrors M1 to M6 are exposed to the illumination light 3 with ineach case a particular spectrum of incidence angles. Said spectrum ofincidence angles is the difference between a smallest incidence angleα_(min) and a largest incidence angle α_(max) impinging the respectivemirror M1 to M6. This is shown in FIG. 2 by the example of the secondlast mirror M5 which has the greatest absolute spectrum of incidenceangles of the projection optics 7.

The following table shows the spectrum of incidence anglesα_(max)-α_(min) of the mirrors M1 to M6:

Mirror α_(max) − α_(min) M1 4.4° M2 5.5° M3 2.3° M4 2.2° M5  10° M6 9.6°

In the meridional section of FIG. 2, the smallest incidence angleα_(min), which amounts to approximately 14°, can be found on theright-hand edge of the mirror M5. The largest incidence angle α_(max) ofFIG. 2, amounts to approximately 24°, can be found on the left-hand edgeof the mirror M5. Therefore, the mirror M5 has a spectrum of incidenceangles of 10°. This spectrum of incidence angles is at the same time thegreatest difference between the incidence angles impinging one of themirrors M1 to M6. The incidence angles impinging the mirrors M1 to M6 ofthe projection optics 7 are almost exclusively in a range of excellentfulfillment of the approximation of small angles (0°≦α≦7°). Therefore,the mirrors M1 to M6 are coated with a reflective coating which isevenly applied across their entire reflecting surface.

The reflective coating is in particular a multilayer coating, in otherwords a stack of alternating molybdenum and silicon layers as is usualfor EUV reflective coatings. The small spectrum of maximum incidenceangles of only 10° ensures that the reflections on all mirrors M1 and M6are constant in good approximation. An unwanted variation in reflectionacross the respective mirror surface or an excessive apodization is thusavoided in the projection optics 7. Apodization is defined as thevariation of the intensity distribution of the illumination light 3across the pupil. If I_(max) is the maximum intensity of theillumination light 3 in a pupil plane of the projection optics 7 andI_(min), is the minimum intensity of the illumination light 3 acrosssaid pupil plane, the value

A=(I _(max) −I _(min))I _(max)

is a measure of apodization.

At least one of the mirrors M1 to M6 has a reflecting surface which is afreeform reflecting surface having a biconical basic shape and which maybe described using the following surface formula:

$z = {\frac{{{cvx} \cdot x^{2}} + {{cvy} \cdot y^{2}}}{1 + \sqrt{1 - {{{cvx}^{2}( {{ccx} + 1} )}x^{2}} - {{{cvy}^{2}( {{ccy} + 1} )}y^{2}}}} + {\sum\limits_{i = 0}^{n}{\sum\limits_{j = 0}^{i}{\alpha_{j,{i - j}}x^{j}y^{i - j}}}}}$

x and y represent the coordinates on the reflecting surface startingfrom a coordinate origin which is defined as the penetration point of anormal through the reflecting surface. In theory, this penetration pointmay be disposed beyond the useful reflecting surface.

z represents the sagittal height of the freeform reflecting surface. Thecoefficients cvx and cvy describe the curvatures of the freeformreflecting surface in an xy sectional view and in an xz sectional view.The coefficients ccx and ccy are conical parameters.

The freeform surface formula is composed of a first biconical term and asubsequent xy polynomial with coefficients a_(ji).

The following tables specify the arrangement and shape of the opticalsurfaces of the mirrors M1 to M6 in the projection optics 7.

In the first column of table 1, selected surfaces are denoted bynumbers. The second column contains the respective distances of eachsurface from the respectively nearest surface in the z-direction. Thethird column of table 1 lists respective y-decentrations of the localcoordinate system of each surface with respect to a global coordinatesystem.

The last column of table 1 allows the defined surfaces to be allocatedto the components of the projection optics 7.

TABLE 1 Distance from preceding Surface surface y-decentration 00.000000 0 image plane 1 708.322803 0 2 −617.533694 −91.468948 M6 3583.375491 −91.682056 M5 4 −593.218566 −91.059467 M4 5 648.730180−155.250886 M3 6 −403.572644 −96.008370 M2 7 674.571026 −73.556295 M1 80.000000 −656.479198 object plane

Table 2 contains the data of the respective freeform reflecting surfaceof the mirrors M6 (surface 2), M5 (surface 3), M4 (surface 4), M3(surface 5), M2 (surface 6) and M1 (surface 7). Coefficients which arenot listed in the table equal zero. Furthermore, the following applies:RDX=1/cvx; RDY=1/cvy.

TABLE 2 Freeform data Surface 2 RDY −970.864728 RDX −994.977890 CCY0.433521 CCX 0.477907 j i-j a_(j, i-j) 0 1 −1.160933E−03 2 0−2.807756E−05 0 2 −2.400704E−05 2 1 −2.727535E−10 0 3 −1.561712E−09Surface 3 RDY −859.920276 RDX −909.711920 CCY 2.066084 CCX 2.157360 ji-j a_(j, i-j) 0 1 −6.956243E−03 2 0 4.069558E−04 0 2 4.110308E−04 2 1−1.135961E−08 0 3 −3.068762E−08 Surface 4 RDY 2123.400000 RDX1668.900000 CCY 11.575729 CCX 7.435682 j i-j a_(j, i-j) 0 1 1.393833E−012 0 3.570289E−04 0 2 4.726719E−04 2 1 4.922014E−08 0 3 1.301911E−09Surface 5 RDY 1292.100000 RDX 1411.600000 CCY −0.067691 CCX 0.332429 ji-j a_(j, i-j) 0 1 2.827164E−03 2 0 3.218435E−05 0 2 6.355344E−07 2 13.212318E−09 0 3 3.463152E−09 Surface 6 RDY −2615.500000 RDX−11975.000000 CCY 0.354474 CCX 58.821858 j i-j a_(j, i-j) 0 1−1.510373E−01 2 0 2.929133E−04 0 2 3.971921E−04 2 1 −2.211237E−08 0 32.084484E−08 Surface 7 RDY 171.052222 RDX 507.844993 CCY −1.000256 CCX−1.006263 j i-j a_(j, i-j) 0 1 1.224307E−02 2 0 −7.916373E−04 0 2−2.757507E−03 2 1 −3.313700E−08 0 3 −7.040288E−09

FIG. 3 shows another embodiment of a projection optics 14 which may beused in the projection exposure apparatus 1 according to FIG. 1 insteadof the projection optics 7. Components of the projection optics 14 whichcorrespond to those that have already been explained above in relationto the projection optics 7 have the same reference numerals and are notdescribed in detail again.

The projection optics 14 has a numerical aperture of 0.25 on the imageside. The overall length T of the projection optics 14 amounts to 1000mm. The object image shift d_(OIS) of the projection optics 14 amountsto 656.5 mm. Therefore, the ratio of T/d_(OIS) amounts to approximately1.52.

In the projection optics 14, the spectrum of maximum incidence angles,which amounts to 12°, can be found on the mirror M5 as well. The minimumincidence angle, which amounts to approximately 6°, is found on themirror M5 on the right-hand edge of FIG. 3. The maximum incidence angle,which amounts to approximately 18°, is found on the mirror M5 on theleft-hand edge of FIG. 3. In the projection optics 14, the image plane 9is the first field plane downstream of the object plane 5 as well.

In the projection optics 14, at least one of the mirrors M1 to M6 is abiconical freeform reflecting surface as well.

The following tables specify the arrangement and shape of the opticalsurfaces of the mirrors M1 to M6 in the projection optics 14. In thefirst column of table 3, selected surfaces are denoted by numbers. Thesecond column contains the respective distances of each surface from therespective nearest surface in the z-direction. The third column of table3 lists respective y-decentrations of the local coordinate system ofeach surface with respect to a global coordinate system.

The last column of table 3 allows the defined surfaces to be allocatedto the components of the projection optics 14.

TABLE 3 Distance from preceding Surface surface y-decentration 00.000000 0 image plane 1 636.883689 0 2 −584.268871 −127.232050 M6 3649.268844 −127.625397 M5 4 −689.518581 −127.310875 M4 5 635.140406−214.759354 M3 6 −438.983578 −160.525812 M2 7 792.496449 −161.853347 M18 0.000000 −978.074419 object plane

Table 4 contains the data of the respective freeform reflecting surfaceof the mirrors M6 (surface 2), M5 (surface 3), M4 (surface 4), M3(surface 5), M2 (surface 6) and M1 (surface 7). Coefficients which arenot listed in the table equal zero. Furthermore, the following applies:RDX=1/cvx; RDY=1/cvy.

TABLE 4 Freeform data Surface 2 RDY −1024.300000 RDX −1051.200000 CCY0.715756 CCX 0.739924 j i-j a_(j, i-j) 0 1 −7.576779E−04 2 0−3.738732E−05 0 2 −4.247383E−05 2 1 9.295774E−10 0 3 −2.890724E−09 4 0−7.975116E−13 2 2 −5.165327E−12 0 4 3.661841E−13 4 1 −7.996231E−16 2 32.111768E−15 0 5 −1.722248E−15 6 0 −5.045304E−19 4 2 5.124801E−18 2 46.369116E−18 0 6 −1.032383E−18 Surface 3 RDY −1035.900000 RDX−1101.300000 CCY 2.617124 CCX 2.951155 j i-j a_(j, i-j) 0 1−2.179019E−03 2 0 4.431389E−04 0 2 4.560760E−04 2 1 −1.644268E−08 0 3−2.950490E−08 4 0 2.263165E−11 2 2 1.778578E−11 0 4 1.964554E−12 4 11.279827E−14 2 3 6.648394E−14 0 5 −2.265488E−14 6 0 2.095952E−17 4 24.287989E−17 2 4 −1.642439E−17 0 6 −2.118969E−17 Surface 4 RDY1665.900000 RDX 1372.000000 CCY 9.138623 CCX 1.926620 j i-j a_(j, i-j) 01 2.014437E−01 2 0 2.109164E−04 0 2 4.684147E−04 2 1 1.447739E−09 0 33.484838E−09 4 0 −1.165581E−24 2 2 4.175896E−13 0 4 7.119405E−12 4 15.269322E−14 2 3 −2.420761E−14 0 5 −2.012170E−14 6 0 −3.454027E−16 4 21.557629E−16 2 4 −1.050420E−15 0 6 −2.742748E−17 Surface 5 RDY1238.200000 RDX 1414.200000 CCY −0.000012 CCX 0.119482 j i-j a_(j, i-j)0 1 1.047982E−02 2 0 2.196150E−05 0 2 7.186632E−07 2 1 4.040466E−09 0 39.100125E−09 4 0 5.634656E−12 2 2 −2.298266E−14 0 4 −4.645176E−13 4 19.046464E−16 2 3 −2.605868E−16 0 5 −1.673891E−15 6 0 −2.618503E−18 4 24.839689E−18 2 4 −6.947211E−18 0 6 −4.314040E−18 Surface 6 RDY−3684.400000 RDX −3506.300000 CCY −0.001235 CCX 0.415150 j i-ja_(j, i-j) 0 1 −1.767860E−01 2 0 5.073838E−04 0 2 5.272916E−04 2 1−3.957421E−08 0 3 8.058238E−09 4 0 7.959552E−25 2 2 −7.112502E−13 0 46.827653E−13 4 1 −2.253930E−13 2 3 1.303253E−13 0 5 1.567942E−15 6 0−2.326019E−16 4 2 −2.314170E−16 2 4 1.309455E−16 0 6 −5.879379E−18Surface 7 RDY 167.705178 RDX 408.126726 CCY −1.001961 CCX −0.994641 ji-j a_(j, i-j) 0 1 −2.378224E−04 2 0 −1.003186E−03 0 2 −2.870643E−03 2 1−3.511331E−09 0 3 −1.211650E−07 4 0 −7.010621E−11 2 2 −5.812898E−12 0 4−4.637999E−13 4 1 −1.913197E−13 2 3 6.243649E−16 0 5 4.280774E−16 6 0−5.399656E−17 4 2 −1.237113E−16 2 4 1.580174E−19 0 6 6.222451E−19

FIG. 4 shows another embodiment of a projection optics 15 which may beused in the projection exposure apparatus according to FIG. 1 instead ofthe projection optics 7. Components of the projection optics 15 whichcorrespond to those that have already been explained above in relationto the projection optics 7 have the same reference numerals and are notdiscussed in detail again.

The projection optics 15 has a numerical aperture of 0.32 on the imageside. The overall length T of the projection optics 15 amounts to 1,000mm. The object image shift d_(OIS) of the projection optics 15 amountsto 978 mm. The ratio of T/d_(OIS) therefore amounts to approximately1.02.

In the projection optics 15, the spectrum of maximum incidence angles,which amounts to 13°, can be found on the mirror M5 as well. The minimumincidence angle, which amounts to approximately 9°, is found on themirror M5 on the right-hand edge of FIG. 4. The maximum incidence angle,which amounts to approximately 22°, is found on the mirror M5 on theleft-hand edge of FIG. 4. In the projection optics 15, the image plane 9is the first field plane downstream of the object plane 5 as well.

In the projection optics 15, at least one of the mirrors M1 to M6 is abiconical freeform reflecting surface as well.

The following tables specify the arrangement and shape of the opticalsurfaces of the mirrors M1 to M6 in the projection optics 15.

In the first column of table 5, selected surfaces are denoted bynumbers. The second column contains the respective distances of eachsurface from the respective nearest surface in the z-direction. Thethird column of table 5 lists respective y-decentrations of the localcoordinate system of each surface with respect to a global coordinatesystem.

The last column of table 5 allows the defined surfaces to be allocatedto the components of the projection optics 15.

TABLE 5 Distance to preceding Surface surface y-decentration 0 0.0000000.000000 image plane 1 726.023335 0.000000 2 −577.595015 −192.238869 M63 745.417411 −192.777551 M5 4 −738.103985 −192.462469 M4 5 994.730526−243.767917 M3 6 −450.919688 −164.949143 M2 7 885.694809 −165.918838 M18 0.000000 −1114.493643 object plane

Table 6 contains the data of the respective freeform reflecting surfaceof the mirrors M6 (surface 2), M5 (surface 3), M4 (surface 4), M3(surface 5), M2 (surface 6) and M1 (surface 7). Coefficients which arenot listed in the table equal zero. Furthermore, the following applies:RDX=1/cvx; RDY=1/cvy.

TABLE 6 Freeform data Surface 2 RDY −1172.300000 RDX −1295.000000 CCY0.787469 CCX 1.053600 j i-j a_(j, i-j) 0 1 −7.219074E−04 2 0−3.578974E−05 0 2 −2.128273E−05 2 1 7.097815E−10 0 3 −1.618913E−09 4 0−2.252005E−12 2 2 −3.895991E−12 0 4 2.750606E−13 4 1 −4.464498E−15 2 3−4.637860E−16 0 5 −6.920120E−16 6 0 −3.637297E−18 4 2 2.537830E−18 2 41.002850E−17 0 6 −3.044197E−18 Surface 3 RDY −1236.400000 RDX−1536.200000 CCY 2.551177 CCX 4.047183 j i-j a_(j, i-j) j 0 1−6.558677E−03 2 0 3.540129E−04 0 2 4.133618E−04 2 1 −1.904320E−08 0 3−3.576692E−08 4 0 1.496417E−12 2 2 1.864663E−11 0 4 3.000005E−12 4 1−7.105811E−15 2 3 5.293727E−14 0 5 −1.509974E−14 6 0 2.907360E−18 4 25.694619E−17 2 4 8.177232E−17 0 6 4.847943E−18 Surface 4 RDY 2267.500000RDX 1709.200000 CCY 13.716154 CCX 2.188445 j i-j a_(j, i-j) 0 12.536301E−01 2 0 1.786226E−04 0 2 4.303983E−04 2 1 −5.494928E−10 0 34.116436E−09 4 0 −2.775915E−11 2 2 3.269596E−11 0 4 3.121929E−12 4 12.286620E−14 2 3 1.431437E−14 0 5 −8.016660E−15 6 0 −8.966865E−17 4 23.631639E−16 2 4 −3.150250E−16 0 6 −7.235944E−18 Surface 5 RDY1453.100000 RDX 1691.600000 CCY 0.004158 CCX 0.130787 j i-j a_(j, i-j) 01 1.413720E−02 2 0 1.853431E−05 0 2 8.632041E−07 2 1 2.471907E−09 0 31.031600E−08 4 0 1.594814E−12 2 2 1.271047E−13 0 4 −8.477699E−14 4 11.841514E−15 2 3 1.063273E−15 0 5 −3.890516E−16 6 0 −7.937130E−19 4 24.923627E−18 2 4 −3.489821E−18 0 6 −3.625541E−18 Surface 6 RDY−3061.000000 RDX −3961.700000 CCY 0.069638 CCX 0.416068 j i-j a_(j, i-j)j 0 1 −1.950186E−01 2 0 4.908498E−04 0 2 5.948960E−04 2 1 −2.711540E−080 3 1.073427E−08 4 0 −3.053221E−12 2 2 −5.601149E−12 0 4 4.072326E−13 41 −3.675214E−13 2 3 3.165916E−14 0 5 −1.649353E−15 6 0 −8.908751E−17 4 2−2.427088E−16 2 4 2.643106E−16 0 6 −7.400900E−18 Surface 7 RDY210.148013 RDX 383.382688 CCY −1.001702 CCX −0.999069 j i-j a_(j, i-j) 01 −2.506963E−04 2 0 −1.093695E−03 0 2 −2.285463E−03 2 1 −7.246135E−09 03 −1.030905E−07 4 0 −7.535621E−11 2 2 −4.600461E−12 0 4 −9.217052E−14 41 −2.057821E−13 2 3 2.433632E−16 0 5 1.627316E−16 6 0 −1.969282E−17 4 2−1.033559E−16 2 4 2.086873E−17 0 6 1.058816E−18

FIG. 5 shows another embodiment of a projection optics 16 which may beused in the projection exposure apparatus 1 according to FIG. 1 insteadof the projection optics 7. Components of the projection optics 16 whichcorrespond to those that have already been explained above in relationto the projection optics 7 have the same reference numerals and are notdiscussed in detail again.

The projection optics 16 has a numerical aperture of 0.35 on the imageside. The overall length T of the projection optics 16 amounts to 1,500mm. The object image shift d_(OIS) of the projection optics 16 amountsto 580 mm. The ratio of T/d_(OIS) therefore amounts to approximately2.59.

On the mirror M5 of the projection optics 16, there is a minimumincidence angle of 0.15° and a maximum incidence angle of 23.72°. Thespectrum of maximum incidence angles, which is found on the mirror M5,therefore amounts to 23.58°, which is the greatest spectrum of incidenceangles to be found on one of the mirrors of the projection optics 16.

The projection optics 16 has an intermediate image plane 17 between themirrors M4 and M5. Said intermediate image plane 17 is approximatelydisposed at the point where the imaging beams 13 are guided past themirror M6.

The freeform reflecting surfaces of the mirrors M1 to M6 of theprojection optics 16 can be described mathematically by the followingequation:

$Z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {( {1 + k} )c^{2}r^{2}}}} + {\sum\limits_{j = 2}^{N}{C_{j}X^{m}Y^{n}}}}$with $j = {\frac{( {m + n} )^{2} + m + {3n}}{2} + 1}$

Z represents the sagittal height of the freeform surface at the point x,y (x²+y²=r²).

c is a constant which corresponds to the apex curvature of acorresponding asphere. k corresponds to a conical constant of acorresponding asphere. C_(j) are the coefficients of the monomialsX^(m)Y^(n). Typically, the values of c, k and C_(j) are determined onthe basis of the desired optical properties of the mirror in theprojection optics 16. The order of the monomial, m+n, can be changed asrequired. A higher-order monomial may result in a design of theprojection optics which facilitates the correction of imaging errors butis more difficult to calculate. m+n may take values between 3 and morethan 20.

Freeform surfaces can also be described mathematically using Zernikepolynomials which are for instance explained in the manual of theoptical design program CODE V®. Alternatively, freeform surfaces can bedescribed using of two-dimensional spline surfaces. Examples thereof areBezier curves or non-uniform rational basis splines (NURBS).Two-dimensional spline surfaces can for instance be described by a setof points in an xy plane and their respective z values or by thesepoints and their respective slopes. Depending on the type of splinesurface, the entire surface is obtained by interpolation between thepoints of the set by using for instance polynomials or functions whichhave particular properties in terms of their continuity anddifferentiability. Examples thereof are analytical functions.

The optical design data of the reflecting surfaces of the mirrors M1 toM6 of the projection optics 16 are listed in the following tables. Thefirst one of these tables contains the respective reciprocal of the apexcurvature (radius) and a distance value (thickness) for the opticalsurfaces of the optical components and for the aperture diaphragm, thedistance value corresponding to the z-distance of adjacent elements inthe beam path starting from the object plane. The second table containsthe coefficients C_(j) of the monomials X^(m)Y^(n) in the above freeformsurface equation for the mirrors M1 to M6, with Nradius being anormalizing constant. The second table is followed by a third table inwhich are listed the absolute values (in mm) of y-decentration andx-rotation of the respective mirror with respect to a reference designof a mirror. This corresponds to the processes of decentration (in they-direction) and rotation (about the x-axis) during the freeform surfacedesign process, with the angle of rotation being specified in degrees.

Surface Radius Distance Mode of operation Object plane INFINITY 727.645Mirror 1 −1521.368 −420.551 REFL Mirror 2 4501.739 540.503 REFL Mirror 3501.375 −313.416 REFL Mirror 4 629.382 868.085 REFL Mirror 5 394.891−430.827 REFL Mirror 6 527.648 501.480 REFL Image plane INFINITY 0.000Coefficient M1 M2 M3 M4 M5 M6 K −6.934683E+00 −1.133415E+02−4.491203E+00 2.864941E−01 6.830961E+00 8.266681E−02 Y 0.000000E+000.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 X2−1.784786E−04 −1.625398E−04 −4.091759E−04 −1.283213E−05 1.852188E−041.527974E−06 Y2 −1.924874E−04 −2.007476E−04 −4.089273E−04 −3.385713E−051.462618E−04 1.999354E−06 X2Y 7.567253E−08 3.033726E−07 4.563127E−073.550829E−08 2.779793E−07 6.063643E−10 Y3 4.318244E−08 4.548440E−09−4.162578E−08 −2.113434E−08 6.705950E−07 5.861708E−09 X4 −4.430972E−10−1.014203E−09 4.055457E−09 −6.220378E−11 −8.891669E−10 −1.395997E−11X2Y2 −8.520546E−10 −6.881264E−10 8.939911E−09 −1.392199E−10 5.141975E−09−1.167067E−11 Y4 −4.543477E−10 9.382921E−10 5.474325E−09 −6.995794E−115.400196E−10 3.206239E−12 X4Y −2.099305E−14 −4.394241E−13 −5.095787E−12−1.116149E−14 −3.574353E−13 5.504390E−15 X2Y3 −9.594625E−14−5.563377E−12 −2.467721E−12 1.007439E−14 1.351005E−11 1.988648E−14 Y5−6.552756E−13 −1.586808E−11 3.433129E−11 1.283373E−12 5.833169E−118.273816E−15 X6 −5.518407E−17 −4.175604E−15 −2.733992E−14 −9.578075E−17−7.907746E−14 −2.844119E−17 X4Y2 1.982470E−16 5.202976E−15 −3.722675E−141.225726E−16 2.278266E−14 −2.154623E−17 X2Y4 3.530434E−16 2.469563E−14−2.047537E−13 −1.207944E−15 2.530016E−13 2.350448E−18 Y6 1.142642E−152.708016E−14 −7.131019E−34 1.880641E−14 1.622798E−13 −9.962638E−18 X6Y−6.790512E−20 −1.328271E−17 −2.926272E−16 −2.248097E−19 −4.457988E−168.532237E−21 X4Y3 −6.322471E−19 3.908456E−17 −2.737455E−16 −7.629602E−201.416184E−15 3.243375E−20 X2Y5 −1.195858E−17 −5.908420E−17 6.146576E−151.102606E−16 3.414825E−15 −2.740056E−21 Y7 2.350101E−17 −1.477424E−155.232866E−14 1.218965E−15 1.819850E−15 −1.903739E−19 X8 −6.917298E−228.248359E−20 6.770710E−19 9.667078E−22 −3.953231E−39 −4.407667E−23 X6Y2−4.633739E−22 1.268409E−19 −1.035701E−18 −6.006155E−20 2.725218E−38−6.933821E−23 X4Y4 −1.497254E−20 −1.719209E−18 −3.217683E−18−1.742201E−20 −1.679944E−39 4.964397E−23 X2Y6 −3.969941E−20−3.497307E−18 4.228227E−17 −2.656234E−18 4.611895E−18 1.663632E−22 Y86.708554E−20 1.187270E−18 2.685040E−38 −1.611964E−39 4.730942E−186.011162E−23 X8Y −4.466562E−24 3.597751E−23 2.879249E−20 −1.588496E−23−5.662885E−20 5.805689E−26 X6Y3 2.874487E−23 1.003878E−20 6.793162E−203.438183E−23 −1.071225E−20 −1.310631E−25 X4Y5 2.249612E−23 1.390470E−201.950655E−19 1.008316E−21 −6.062162E−20 −3.380438E−25 X2Y7 5.258895E−222.194560E−20 −2.724912E−18 −3.405763E−20 −1.780372E−19 1.649113E−25 Y9−4.497858E−21 2.311634E−19 −2.656603E−17 −3.124398E−19 −1.417439E−192.296226E−24 X10 0.000000E+00 −6.351950E−24 −8.560053E−23 −4.339912E−26−8.430614E−22 −3.388610E−28 X8Y2 0.000000E+00 4.523937E−24 9.792140E−222.952972E−24 9.614763E−23 1.083831E−27 X6Y4 0.000000E+00 −9.774541E−23−2.428620E−21 −5.303412E−24 −1.020095E−22 3.199302E−27 X4Y6 0.000000E+004.704150E−23 1.195308E−42 2.279968E−23 −6.658041E−23 1.968405E−27 X2Y80.000000E+00 1.270549E−22 1.329832E−41 8.858543E−22 5.185397E−223.257732E−28 Y10 0.000000E+00 −1.244299E−21 −8.254524E−44 −6.003123E−225.204197E−23 1.473250E−27 NRadius 1.000000E+00 1.000000E+00 1.000000E+001.000000E+00 1.000000E+00 1.000000E+00 Coefficient M1 M2 M3 M4 M5 M6Image Y-Decentration 37.685 −15.713 −139.004 −151.477 −395.184 −440.9210.000 X-Rotation 0.326 −3.648 −5.539 −5.647 4.878 5.248 0.000

In FIG. 5, the reference numeral 18 denotes a chief ray which isallocated to a central object field point. The reference numeral 19refers to a normal to the object plane 5 in FIG. 5, said normal passingthrough the central object field point. In other words, the chief ray 18and the normal 19 intersect in the object plane 5. When the chief ray 18continues to propagate along its path between the object plane 5 and theimage plane 9, the distance of the chief ray 18 from the normal 19increases monotonically. When the chief ray 18 passes through the imageplane, in other words in the central image field point, this distance isidentical to the object image shift d_(OIS). As the distance of thechief ray 18 from the normal 19 increases monotonically along the beampath between the object plane 5 and the image plane 9, there will be nodecrease in distance along the entire beam path. In the projectionoptics 16, this distance increases continuously until the chief ray 18impinges upon the last mirror M6. Between the point of incidence of thechief ray 18 on the mirror M6 and the image plane 9, this distanceremains constant.

FIG. 6, which is less diagrammatic than FIG. 1, shows the projectionexposure apparatus 1 which is equipped with the projection optics 16.Components, which correspond to those that have already been explainedabove in relation to FIGS. 1 to 5 in particular, have the same referencenumerals and are not discussed in detail again.

Having been emitted by the light source 2, the illumination light 3 isinitially collected by a collector 20 which is illustrateddiagrammatically in FIG. 6.

In contrast to the illustration according to FIG. 1, the illustrationaccording to FIG. 6 shows the light source 2 on a level which is belowthe level of the image plane 9 in FIG. 6. The illumination light 3collected by the collector 20 therefore needs to be guided past thesubstrate holder 12.

In the embodiment according to FIG. 6, the illumination optics 6includes a field facet mirror 21 which is disposed downstream of thecollector 20, and a pupil facet mirror 22 which is disposed downstreamof said field facet mirror 21. The two facet mirrors 21, 22 are used toachieve a defined setting of an intensity distribution and of anillumination angle distribution of the illumination light 3 across theobject field 4. Between the collector 20 and the field facet mirror 21,there is an intermediate focus 23 which is disposed in the beam path ofthe illumination light 3. The large object image shift d_(OIS) of theprojection optics 16 according to FIGS. 5 and 6 allows the beam path toextend normally, in other words vertically, to the object plane 5 and tothe image plane 9. Excessively large incidence angles on the mirrorsguiding the illumination light 3 are therefore not required for guidingthe illumination light 3 past the substrate holder 12.

The projection exposure apparatus 1 including the projection optics 16according to FIG. 6 has an intermediate-focus image shift D of 855 mm.The intermediate-focus image shift D is defined as the distance of acentral point of the image field 8 form a penetration point of a normalfrom the intermediate focus 23 to the image plane 9.

A ratio between the overall length T of the projection optics 16 and theintermediate-focus image shift D amounts to T/D=1.75 in the projectionexposure apparatus 1 according to FIG. 6.

FIG. 7 is a similar illustration to FIG. 6 of a projection exposureapparatus 1 including the projection optics 16 according to FIG. 6 andincluding another embodiment of an illumination optics 6. Componentswhich correspond to those that have already been explained above inrelation to FIGS. 1 to 6, in particular to FIG. 6, have the samereference numerals and are not discussed in detail again.

In contrast to the illumination optics 6 of the embodiment according toFIG. 6, the embodiment according to FIG. 7 includes a pupil facet mirror22 with a through opening 24 for the illumination light 3. Theillumination light 3 passes through the through opening 24 along thebeam path between the collector 20 and the field facet mirror 21. In theembodiment according to FIG. 7, the intermediate focus 23 is disposed inthe vicinity of the through opening 24.

In the projection exposure apparatus 1 according to FIG. 7, anintermediate-focus image shift D amounts to 703 mm. Therefore, a ratiobetween the overall length T of the projection optics 16, which isidentical to the projection optics 16 according to FIG. 6, and theintermediate-focus image shift D amounts to T/D=2.12.

The beam path between the collector 20 and the field facet mirror 21makes an angle γ of 81° with the object plane 5 and with the image plane9. Consequently, the beam path deviates from the normal by only 9°.

Using the illumination optics 6 according to FIG. 7, a particularlysmall maximum incidence angle of the illumination light 3 impinging uponthe field facet mirror 21 is achieved.

The projection optical systems 7, 14, 15 and 16 are bundle-guidingcomponents and therefore include only mirrors. These projection opticalsystems 7, 14, 15, 16 are therefore referred to as mirror projectionobjectives.

When producing a microstructured component using the projection exposureapparatus 1, the reflection mask 10 and the substrate 11 are provided ina first step. Afterwards, a structure on the reflection mask 10 isprojected onto a light-sensitive layer on the wafer 11 using theprojection optics 7, 14, 15 or 16 of the projection exposure apparatus1. The light-sensitive layer is then developed into a micro-structure onthe wafer 11 which is then developed into the microstructured component.

Other embodiments are in the following claims.

1. A projection objective for imaging an object field in an object planeinto an image field in an image plane, the projection objectivecomprising at least six mirrors of which at least one mirror has afreeform reflecting surface, wherein the projection objective is amicrolithography projection objective and has an overall length, T, andan object image shift, d_(OIS), where T is the distance between theobject plane and the image plane along an axis and d_(OIS) is thedistance of a projection perpendicular to the object plane of a centralobject field point onto the image plane from the corresponding point inthe image field, where a ratio of T to d_(OIS) is smaller than
 12. 2.The projection objective according to claim 1, wherein the ratio of T tod_(OIS) is smaller than
 5. 3. The projection objective according to oneof claims 1, wherein the freeform reflecting surface is a biconicalsurface.
 4. The projection objective according to claim 1, wherein adistance between a chief ray of a central point of the object field anda normal to the object plane, the normal passing through the centralpoint of the object plane increases monotonically along a path of thechief ray which starts at the object field and propagates to the imagefield.
 5. The projection objective according to claim 1, wherein d_(OIS)is greater than 200 mm.
 6. The projection objective according to claim1, wherein during operation the projection objective directs light alonga path from the object field to the image field and a ratio of adifference between a largest and a smallest incidence angle of the lightimpinging upon one of the mirrors to a numerical aperture on the imageside of the projection objective is 60° or less.
 7. The projectionobjective according to claim 1, wherein a numerical aperture on theimage side of the projection objective is at least 0.25
 8. Theprojection objective according to claim 1, wherein the object fieldand/or image field have dimensions of at least 2 mm×26 mm.
 9. Theprojection objective according to claim 1, wherein during operation theprojection objective directs light along a path from the object field tothe image field and an incidence angle of the light that at the centralobject field point is in a range between 5° and 9°.
 10. A projectionobjective for imaging an object field in an object plane into an imagefield in an image plane, the projection objective comprising: aplurality of mirrors, wherein the projection objective is amicrolithography projection objective and wherein the projectionobjective is a microlithography projection objective and has an overalllength, T, and an object image shift, d_(OIS), where T is the distancebetween the object plane and the image plane along an axis and d_(OIS)is the distance of a projection perpendicular to the object plane of acentral object field point onto the image plane from the correspondingpoint in the image field, where a ratio of T to d_(OIS) is smaller than2.
 11. The projection objective according to claim 10, wherein theplurality of mirrors comprise at least six mirrors.
 12. The projectionobjective according to claim 10, wherein at least one of the mirrors hasa freeform reflecting surface.
 13. The projection objective according toclaim 12, wherein the freeform reflecting surface is a biconicalsurface.
 14. The projection objective according to claim 13, wherein theimage plane is the first field plane of the projection objectivedownstream of the object plane.
 15. The projection objective accordingto claim 10, wherein a distance between a chief ray of the centralobject field point and a normal to the object plane, the normal passingthrough the central point of the object plane increases monotonicallyalong a path of the chief ray which starts at the object field andpropagates to the image field.
 16. The projection objective according toclaim 10, wherein d_(OIS) is greater than 200 mm.
 17. The projectionobjective according to claim 10, wherein during operation the projectionobjective directs light along a path from the object field to the imagefield and a ratio of a difference between a largest and a smallestincidence angle of the light impinging upon one of the mirrors to anumerical aperture on the image side of the projection objective is 60°or less.
 18. The projection objective according to claim 10, wherein anumerical aperture on the image side of the projection objective is atleast 0.25
 19. The projection objective according to claim 10, whereinthe object field and/or image field have dimensions of at least 2 mm×26mm.
 20. The projection objective according to claim 10, wherein duringoperation the projection objective directs light along a path from theobject field to the image field and an incidence angle of the light thatat the central object field point is in a range between 5° and 9°.
 21. Aprojection objective for imaging an object field in an object plane intoan image field in an image plane, the projection objective comprising:at least six mirrors of which at least one mirror has a freeformreflecting surface, wherein the projection objective is amicrolithography projection objective and the image plane is the firstfield plane of the projection objective downstream of the object plane.22. The projection objective according to claim 21, wherein theprojection objective has an overall length, T, and an object imageshift, d_(OIS), where T is the distance between the object plane and theimage plane along an axis and d_(OIS) is the distance of a projectionperpendicular to the object plane of a central object field point ontothe image plane from the corresponding point in the image field, where aratio of T to d_(OIS) is smaller than
 5. 23. The projection objectiveaccording to claim 21, wherein the freeform reflecting surface is abiconical surface.
 24. The projection objective according to claim 21,wherein a distance between a chief ray of the central object field pointand a normal to the object plane, the normal passing through the centralpoint of the object plane increases monotonically along a path of thechief ray which starts at the object field and propagates to the imagefield.
 25. The projection objective according to claim 21, whereind_(OIS) is greater than 200 mm.
 26. The projection objective accordingto claim 21, wherein during operation the projection objective directslight along a path from the object field to the image field and a ratioof a difference between a largest and a smallest incidence angle of thelight impinging upon one of the mirrors to a numerical aperture on theimage side of the projection objective is 60° or less.
 27. Theprojection objective according to claim 21, wherein a numerical apertureon the image side of the projection objective is at least 0.25
 28. Theprojection objective according to claim 21, wherein the object fieldand/or image field have dimensions of at least 2 mm×26 mm.
 29. Theprojection objective according to claim 21, wherein during operation theprojection objective directs light along a path from the object field tothe image field and an incidence angle of the light that at the centralobject field point is in a range between 5° and 9°.
 30. A projectionobjective for imaging an object field in an object plane into an imagefield in an image plane, the projection objective comprising: aplurality of mirrors of which at least one mirror has a freeformreflecting surface; at least one intermediate image location between theobject plane and the image plane, wherein the projection objective is amicrolithography projection objective and has an overall length, T, andan object image shift, d_(OIS), where T is the distance between theobject plane and the image plane along an axis and d_(OIS) is thedistance of a projection perpendicular to the object plane of a centralobject field point onto the image plane from the corresponding point inthe image field, where a ratio of T to d_(OIS) is smaller than
 12. 31.The projection objective according to claim 30, wherein the ratiobetween T and d_(OIS) is smaller than
 5. 32. Projection objectiveaccording to claim 30, wherein the freeform reflecting surface isdescribable using the surface equation$Z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {( {1 + k} )c^{2}r^{2}}}} + {\sum\limits_{j = 2}^{N}{C_{j}X^{m}Y^{n}}}}$with $j = {\frac{( {m + n} )^{2} + m + {3n}}{2} + 1}$ Z:sagittal height of the freeform surface at the point x, y (x²+y²=r²); c:constant which represents the apex curvature of a corresponding asphere;k: conical constant of a corresponding asphere; C_(j): coefficients ofthe monomials X^(m)Y^(n).
 33. The projection objective according toclaim 30, wherein a distance between a chief ray of the central objectfield point and a normal to the object plane, the normal passing throughthe central point of the object plane increases monotonically along apath of the chief ray which starts at the object field and propagates tothe image field.
 34. The projection objective according to claim 30,wherein d_(OIS) is greater than 200 mm.
 35. The projection objectiveaccording to claim 30, wherein during operation the projection objectivedirects light along a path from the object field to the image field anda ratio of a difference between a largest and a smallest incidence angleof the light impinging upon one of the mirrors to a numerical apertureon the image side of the projection objective is 60° or less.
 36. Theprojection objective according to claim 30, wherein a numerical apertureon the image side of the projection objective is at least 0.25
 37. Theprojection objective according to claim 30, wherein the object fieldand/or image field have dimensions of at least 2 mm×26 mm.
 38. Theprojection objective according to claim 30, wherein during operation theprojection objective directs light along a path from the object field tothe image field and an incidence angle of the light that at the centralobject field point is in a range between 5° and 9°.
 39. An opticalsystem, comprising: a light source; an illumination system comprisingone or more optical elements; a projection objective arranged to imagean object field in an object plane into an image field in an imageplane, wherein the projection objective and has an overall length, T,and an object image shift, d_(OIS), where T is the distance between theobject plane and the image plane along an axis and d_(OIS) is thedistance of a projection perpendicular to the object plane of a centralobject field point onto the image plane from the corresponding point inthe image field, where a ratio of T to d_(OIS) is smaller than 5, andduring operation the illumination system directs light from the lightsource to the object field and the one or more optical elements of theillumination system are arranged so that the light has an intermediatefocus between the light source and the object field.
 40. The opticalsystem according to claim 39, wherein the projection objective comprisesat least six mirrors of which at least one has a freeform reflectivesurface.
 41. The optical system according to claim 39, wherein at leastone of the optical elements of the illumination system has an openingfor the passage for the passage of the light and the intermediate focusis arranged in the vicinity of the opening.
 42. The optical systemaccording to claim 39, wherein the optical elements of the illuminationsystem comprise a collector and a maximum of three mirrors.
 43. Aprojection exposure apparatus comprising the optical system according toclaim
 39. 44. A method of producing a microstructured component, themethod comprising: providing a reticle and a wafer; projecting astructure on the reticle onto a light-sensitive layer of the wafer usingthe projection exposure apparatus according to claim 41; and creating amicrostructure on the wafer.
 45. A microstructured component producedusing the method according to claim 44.